1. Field of the Invention
The present invention relates in general to a display apparatus, more specifically, to a plasma display apparatus using a plasma display panel.
2. Description of the Related Art
A plasma display apparatus using a plasma display panel (hereinafter referred to as “PDP”) as a display apparatus employs an electromagnetic shield as a measure against electromagnetic interference (EMI) so that unnecessary electromagnetic waves (hereinafter referred to as “unnecessary radiation”) do not leak outside of the apparatus. An electromagnetic wave emitted from the front surface (display surface) of the PDP is shielded by a conductive layer (hereinafter referred to as “electromagnetic shield”) installed at a light-permeable optical filter on the front surface of the PDP. For the purpose of reducing unnecessary radiation, Japanese Patent Laid-Open Publication Nos. 2004-45778 and 2004-170624 disclosed a new scheme for attaching an optical filter that has the aforementioned electromagnetic shield to a plasma display apparatus.
Along with a severe decline in price of PDPs in recent years, a number of PDP manufactures are faced with cutting down their official retailing prices of PDPs. One way to do that is employing a low-price optical filter in replacement of the optical filter equipped with the electromagnetic shield. In general, there are two types of electromagnetic shields: mesh-type electromagnetic shields having conductive metal mesh patterns and transparent conductive film type electromagnetic shields formed by sputtering. The mesh type electromagnetic shields have a surface resistance not higher than 0.1 Ω/square, for example, as described in Table 1 of Japanese Patent Laid-Open Publication No. 2004-221565. On the other hand, the transparent conductive film type electromagnetic shields have a surface resistance not higher than 1.0-2.0 Ω/square as described in Table 3 of Japanese Patent Laid-Open Publication No. 2004-264350.
In the light of the aim of reducing unnecessary radiation, the mesh type electromagnetic shield having a smaller surface resistance is desired. Unfortunately however, the mesh type electromagnetic shield is usually very expensive compared with the transparent conductive film formed by sputtering because an etching process should be carried out for the formation of a metal mesh.
Despite the advantage of cost-effectiveness, the transparent conductive film is still inadequate in some cases for satisfactorily reducing unnecessary radiation due to its relatively high surface resistance. In case of using an optical filter including an electromagnetic shield with a relatively high surface resistance, reducing unnecessary radiation at a satisfactory level becomes very important. However, the above-described conventional technologies do not suggest any fully satisfactory method for reducing unnecessary radiation using a low-price optical filter with a relatively high surface resistance (for example, an optical filter having the transparent conductive film type electromagnetic shield).